1. Field of the Invention
The present invention relates to a preferred base station device and a method of updating a counter of the base station device using a communication system conforming to IEEE 1588 version 2 which is a protocol used to achieve synchronization between devices via a local network such as Ethernet (registered trademark).
2. Description of the Related Art
In a multi-cell digital enhanced cordless telecommunications (DECT) system, in order to seamlessly conduct handover to a slave terminal, it is necessary to achieve precise timing synchronization between base station devices. In a communication system prior to the advent of internet protocol (IP), synchronization was achieved in a wired manner. However, in IP-DECT, since communication is performed through asynchronous Ethernet (registered trademark), air synchronization is achieved not in a wired manner but in a wireless manner.
The IEEE 1588 version 2 defines that when synchronization is established between a base station device as master and a base station device as a slave, a message “Sync” is transmitted from the master base station device every second.
A technology in which synchronization is established using a local network such as Ethernet (registered trade mark) has been known. For example, Japanese Patent Unexamined Publication (Translation of PCT Application) No. 2003-509973 describes a method of achieving synchronization between a plurality of base stations over a mobile communication network. Such a synchronization method of the base stations is a method of achieving synchronization between a plurality of base stations over a mobile communication network. In the synchronization method, time information is transmitted to the plurality of base stations via a local network (LAN), and a clock generator of each of the base stations that receives the time information is adjusted based on time information content of the time information and a reception time, and transmission of a functional sequence related to a wireless time frame is controlled with respect to each base station based on a signal from the clock generator.
However, in order to implement a seamless handover to an IP-DECT client terminal, it is necessary to achieve precise timing synchronization and DECT frame number synchronization between the base station devices in the multi-cell DECT. In the IP-DECT, since communication is performed through the asynchronous Ethernet, synchronization is achieved not in a wired manner but in a wireless manner. However, since the distance between the base station devices is short in the synchronization in the wireless manner, there is a problem in that the number of base station devices is increased, and thus, it may be difficult to provide the base station devices.